Can zonisamide be used in cats?

In this article:

• Zonisamide for cats
• Safety
• Dosage
• Alternatives
• Summary

In this article

• Zonisamide for cats
• Safety
• Dosage
• Alternatives
• Summary

Veterinarians use zonisamide to treat seizure disorders (epilepsy) in cats. It can be used alone, but veterinarians more commonly use it as an add-on therapy with other antiseizure medications. Doses are administered twice daily every day, and treatment can last for years. Side effects are relatively mild, but zonisamide can damage a cat’s liver in rare cases. Zonisamide may require caregivers to monitor their cat for possible signs of liver injury.

RELATED: Save up to 80% on zonisamide

What is zonisamide used for in cats?

Zonisamide therapy reduces seizure frequency and severity in epileptic cats. It can be used as a standalone treatment but is more likely to be prescribed as an add-on therapy in cats with refractory seizures. 

Seizure disorders

A seizure happens when nerves in the brain get overexcited and fire repetitively. For an observer, this neurological overactivity can manifest in several ways: “blanking out,” drooling, vomiting, random facial twitches, running around, tail-chasing, pooping, urinating, muscle rigidity, loss of consciousness, or body-wide convulsions. These seizure episodes are usually brief and last from a few seconds to a few minutes.

Healthy animals do occasionally have seizures. Often, it’s a one-time or temporary problem due to some external problem such as electrolyte imbalances, infections, or poisoning. Veterinarians will bring the seizures under control, examine the cat, perform tests, and treat the underlying cause. 

Seizures are a problem when they happen repeatedly. Repeated seizures are the defining sign of a seizure disorder (epilepsy). Seizure disorders are due to neurological problems (secondary epilepsy) or for no discernible reason (idiopathic epilepsy). Fortunately, recurrent seizure disorders are not very common in cats (about 16 in 10,000), but the incidence increases as a cat ages.  

There is no consensus in veterinary medicine about when a cat should start therapy for epilepsy, but treatment is more likely if seizures are frequent or severe. When therapy is started, the cat will require long-term, daily anticonvulsant therapy to prevent seizures. These are drugs that slow down nerve activity. 

Veterinarians typically start by prescribing one and only one anticonvulsant drug. Using just one drug to treat seizures is called “monotherapy,” and it’s preferable to using two or more drugs because of possible side effects. Veterinarians usually start treating the cat with phenobarbital or levetiracetam. Bromide (potassium bromide or sodium bromide), a common choice in dogs, is not usually used in cats due to the high frequency of severe side effects. 

Monotherapy usually works at controlling a cat’s seizures. When it doesn’t, veterinarians will add other antiepileptic drugs to the treatment regimen. These drugs are called adjuvant (“helping out”) treatments. Veterinarians usually prescribe zonisamide as an adjuvant treatment.

Scientists don’t fully understand zonisamide’s mechanism of action at controlling seizures. Unlike other anticonvulsants, it does not primarily work by slowing down nerve activity. Instead, it seems to stabilize nerve activity by preventing large groups of nerves from firing at the same time. As a result, its sedative effects are not as pronounced as other anticonvulsants.

Zonisamide lasts a long time in a cat, so many guidelines call for once-daily dosing. It’s possible a veterinarian may divide the dose into two daily doses. 

Is zonisamide safe for cats?

Zonisamide is generally safe for cats but should be closely monitored for adverse reactions. Zonisamide may not be safe in cats with liver problems. Side effects seem to be minimal, but the drug has not been extensively studied in small animals.

Zonisamide is contraindicated in cats who:

• Have had an allergic reaction to zonisamide
• Have a known allergy to sulfonamide drugs

Side effects of zonisamide in cats

The most commonly reported side effects of zonisamide in cats are:

• Reduced appetite (inappetence)
• Nausea 
• Vomiting

Zonisamide may also cause drowsiness and incoordination (ataxia) in a cat.

The most serious side effect is liver damage, so cat owners should monitor the cat for signs of hepatic (liver) impairment, including: 

• Complete loss of appetite
• Vomiting
• Diarrhea
• Lethargy
• Excessive thirst
• Excessive urination
• Weight loss
• Yellowing of the eyes or gums

Zonisamide can reduce thyroid hormone levels in cats.

In people, zonisamide can cause other serious adverse effects including:

• High acid levels in the blood (acidosis)
• Electrolyte imbalances

Interactions of zonisamide with other pet meds

To avoid possible drug interactions, tell the veterinarian about all the drugs, herbal remedies, and supplements the cat takes. 

In people, zonisamide can cause problems when combined with:

• Drugs that cause sedation, like opioids, benzodiazepines, sleeping pills, and CBD
• Drugs called carbonic anhydrase inhibitors, such as topiramate, or drugs that treat glaucoma.

In dogs, zonisamide can cause problems when combined with phenobarbital, a first-line treatment for both canine and feline epilepsy. Phenobarbital makes zonisamide less effective in dogs, so veterinarians prescribe higher doses of zonisamide. Phenobarbital doesn’t seem to interact with zonisamide in cats, but a veterinarian may decide to adjust the zonisamide dose anyway. 

Zonisamide dosage for cats

The published veterinary zonisamide dosages for cats are:

• 5 mg/kg given every 12 or 24 hours OR
• 5–10 mg/kg given once daily

For a 10-pound cat, these dosages would work out to 25 to 50 mg, given once or twice daily.

Zonisamide is not FDA-approved for veterinary use. Veterinarians can prescribe capsules formulated for human or veterinary patients, including brand-name Zonegran. Current products are for oral administration only, typically capsules. Unless specially prepared, the standard dosage strengths of zonisamide are 25, 50, and 100 mg per capsule. 

If a liquid formulation is needed, the veterinarian can prescribe a brand-name oral suspension made for people or a generic oil-based liquid version of zonisamide prepared by a compounding pharmacy.

Can cats overdose on zonisamide?

Yes. An overdose can cause serious problems with breathing, blood pressure, or heart rate. If the cat has ingested too much zonisamide, immediately contact an animal poison control center or take the cat to an animal hospital.

Can I give my cat zonisamide every day?

Your cat will take zonisamide every day for months or years as long as it works and doesn’t cause serious side effects. Treatment could last for the cat’s lifetime. 

How to give your cat zonisamide

Cats get one or two doses of zonisamide daily. The veterinarian will require follow-up visits and blood tests to monitor the effectiveness of treatment. Please keep all appointments. Make a record of all the cat’s seizures in a seizure diary and share that information with the veterinarian regularly.

Here are some guidelines for administering zonisamide to your cat:

• Follow all the veterinarian’s directions.
• Do not increase the dose or give doses more often than prescribed.
• Do not discontinue zonisamide until you’ve talked to the veterinarian. The veterinarian will withdraw the medicine in gradually decreasing doses.
• Give doses with or without food. If the cat vomits or gets sick after a dose, try giving doses with food.

• How to give zonisamide capsules to a cat:

• • The capsule should be swallowed whole or can be opened and the contents mixed with a small amount of food. Avoid allowing cat to chew the capsule. 
  • If you’re unsure how to do it, ask a veterinary assistant to demonstrate the best procedure.
  • Store zonisamide capsules at room temperature in a dry place. Protect the medicine from light.

• How to give liquid zonisamide to a cat:

• • The bottle may need to be shaken before measuring a dose.
  • Ask the veterinarian for a calibrated oral syringe or other graduated measuring device. Always use this medicine measuring device to prepare doses.
  • Ask the veterinarian or pharmacist how to properly store zonisamide liquid.

• What to do about a missed dose:

• • Give a missed dose when remembered. 
  • If it’s almost time for the next dose, skip the missed dose. 
  • Give the next dose at its regular time. 
  • Do not administer two doses to make up for a missed dose.

Zonisamide alternatives for cats

Veterinarians use zonisamide either as a first-choice drug for feline seizures or as an add-on treatment with other anticonvulsants. In addition to zonisamide, the preferred standalone treatment for feline seizures is phenobarbital or levetiracetam.

If monotherapy doesn’t achieve seizure control, other medications that can be added to the treatment regimen include: 

• Gabapentin
• Clonazepam
• Topiramate
• Pregabalin

Summary

Veterinarians use zonisamide to control seizures in cats. Because of its unique mechanism of action, toxicity and adverse reactions are less concerning than they are for other anticonvulsants. In rare cases, zonisamide can damage a cat’s liver, so cat caregivers should contact the veterinarian if they notice symptoms such as complete loss of appetite or yellowing of the cat’s eyes or gums.